Many digital communication systems use quadrature techniques, such as quadrature amplitude modulation, because of advantages over other digital modulation techniques. Since most communication systems operate over a range of frequencies, it is necessary to generate quadrature at any frequency in the desired range. Quadrature generation techniques can be classified into either active or passive techniques. Active quadrature splitters, such as digital dividers, are more popular because passive splitters are only truly accurate at one frequency. Deviation from that frequency results in signals that are not 90 degrees apart, which can degrade system performance to the extent that it is unusable.
However, active quadrature generation circuits, although capable of generating quadrature over a range of frequencies, are much more complex than passive quadrature generation circuits. In the personal communications market, low cost is a driving market force, so it is preferable to avoid using complex circuitry when possible. A passive quadrature generation circuit that is operable over a frequency range would be ideal. Therefore there is a need for a means of generating accurate quadrature using passive components that is operable over a range of frequencies.